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1,2,4 and 1,3,4-Oxadiazole Scaffolds in Designing Organic Light-Emitting Diodes 43
Wong, M. Y., S. Krotkus, G. Copley, W. Li, C. Murawski, D. Hall et al. 2018. Deep-blue
oxadiazole-containing thermally activated delayed fluorescence emitters for organic light-emitting
diodes. ACS Appl. Mater. Interfaces 10(39): 33360–33372.
Wu, F.-I., P.-I. Shih, C.-F. Shu, Y.-L. Tung and Y. Chi. 2005. Highly efficient light-emitting diodes based
on fluorene copolymer consisting of triarylamine units in the main chain and oxadiazole pendent
groups. Macromol. 38(22): 9028–9036.
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materials with high thermal stability and triplet energy for efficient phosphorescent OLEDs. Org.
Electron. 27: 126–132.
<XDQ&66DLWR&&DPDFKR6,UOH ,+LVDNLDQG6<DPDJXFKL$ʌFRQMXJDWHGV\VWHPZLWK
IOH[LELOLW\DQGULJLGLW\WKDWVKRZVHQYLURQPHQWGHSHQGHQW5*%OXPLQHVFHQFH-$P&KHP6RF
135(24): 8842–8845.
=KDQJ.<7DR&<DQJ+<RX<=RX-4LQHWDO6\QWKHVLVDQGSURSHUWLHVRIFDUED]ROHPDLQ
chain copolymers with oxadiazole pendant toward bipolar polymer host: tuning the HOMO/LUMO
level and triplet energy. Chem. Mater. 20(23): 7324–7331.
Zhang, X., M. W. Cooper, Y. Zhang, C. Fuentes-Hernandez, S. Barlow, S. R. Marder et al. 2019.
Host-free yellow-green organic light-emitting diodes with external quantum efficiency over 20%
based on a compound exhibiting thermally activated delayed fluorescence. ACS Appl. Mater.
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carbazole-oxadiazole side chains as ambipolar hosts for phosphorescent light-emitting diodes.
Chem. Mater. 23(17): 4002–4015.
Zhao, Y., Q. Guo, X. Li, Q. Wang and D. Ma. 2017. Influence of the linkage mode and D/A ratio of
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-/XPLQ±
Zhou, D., D. Liu, X. Gong, H. Ma, G. Qian, S. Gong et al. 2019. Solution-processed highly efficient
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CHAPTER 3
Oxadiazole as
Liquid Crystals
1. Introduction
For the first time, an Austrian botanist named Fridrich Reinitzer noticed a twofold
melting in cholesteryl benzoate when heated. He discovered that some compounds
underwent birefringence (between crossed polarizers) when heated, and upon
further heating, it turned into a clear liquid (Reinitzer 1888). These substances
later became known as liquid crystals (LCs) by Otto Lehman because they have
both solid and liquid qualities. The LCs’ anisotropic features can be used in optical
displays showing mesophases halfway between solids and liquids (Prakash et al.
2020). Their first generation exhibits that mesophase could only occur in linear (or
rod-shaped) molecules with a finite length-to-breadth (L/B) ratio. Later, it was found
that molecules do not always need to be rod-shaped in order to display mesophases;
instead, non-rod-type molecules can also do so (Chandrasekhar et al. 1977). Then,
the chiral LCs with ferroelectric nature and sub-microsecond responsiveness were
discovered (Ma et al. 2022). Following this, chiral-containing ferroelectric LCs
)/&VZHUHXVHGLQDYDULHW\RIWHFKQLFDODSSOLFDWLRQV*LHȕHOPDQQDQG=XJHQPDLHU
1995; Das et al. 2019). The achiral ferroelectric LCs with non-zero polarization in
external stimuli were synthesized. Due to their efficient synthesis without expensive
chiral components and high yields, the synthesis and characterization of such achiral
FLCs have gained impetus in the recent two decades (Niori et al. 1996; Watanabe
et al. 1998). The melting of these materials is depicted in the accompanying schematic
diagram (Figure 1).
2. Classification of Liquid Crystals
LCs can be categorized based on the change in temperature (thermotropic) or
concentration (lyotropic) (Chavda et al. 2022; Chen et al. 2022). Thermotropic LCs
display a variety of mesophases as a function of temperature. They are crystalline
at low temperatures, whereas above the melting point, they show mesophase
behavior. The ordering of different phases can be destroyed by thermal motion at
high temperatures, turning them into an isotropic liquid phase (Chavda et al. 2022).
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Oxadiazole as Liquid Crystals 45
Figure 1. An illustration of the melting of crystalline material.
Based on their shape, thermotropic LCs are further divided into calamatic (Cakar
et al. 2022), discotic (Khare et al. 2022), polycatenar (Bais et al. 2019), and
bending-shaped (Kumar 2022) LCs. The dissolution of an amphiphile in the solvent
results in the formation of lyotropic LCs. The basic structure of these amphiphile
compounds consists of a polar head and a non-polar tail. These lyotropic LCs
exhibit a variety of phases when the solution concentrations change, and the solvent
molecules fill the area around the structures to keep the system fluid (Fairhurst et al.
1998; Chen et al. 2022). The polarity of the solvent, temperature, and concentration
all affect the lyotropic phase behavior (Burducea 2004). There may be one or more
mesophases present in an LC molecule. Polymesomorphic refers to a compound that
displays more than one mesophase. By adjusting the temperature and concentration,
the lyotropic exhibits different phase variants and hence is called an Amphotropic
LCs. Monotropic occurrence is when an LC compound only displays a phase
sequence during the heating/cooling process. Enantiotropic LC phase occurrence
is defined as being reversible throughout both the heating and cooling runs of the
concentration and dilution processes (Salanger 1999). The classification of liquid
crystals is presented in Figure 2.
Figure 2. Classifications of liquid crystal.
3. Classification of Liquid Crystalline Phases
Based on their optical textures under crossed polarizers and their X-ray diffraction
profiles with temperature fluctuation, various LC phase types can be differentiated
(Carsten 1996). When cooling from the isotropic phase to the crystalline phase, these
LC phases are distinguished by the molecular orientational order of their constituent
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46 Oxadiazole in Material and Medicinal Chemistry
molecules (Elston and Sambles 1998). The most typical LC phase is the nematic (N)
phase, which is regarded as a high-temperature phase. The molecules lack spatial
order but do have long-range orientational order. As a result, the thermotropic phase
is the least organized and is, hence, the closest to an isotropic liquid; they are fluid
enough for molecules to pass one another easily while maintaining their typical
parallel orientations.
Compared to nematics, smectic mesophases exhibit a higher level of order
since the molecules are not only aligned in one direction but also further arranged
into layers. The degree of order present inside and between layers varies between
smectic phases, which exhibit polymorphism. These planes are the only ones where
molecules can move. A large number of chemicals can form more than one type of
smectic phase. However, because the intralayer interactions between the molecules
are stronger than the interlayer forces, the layers are somewhat free to move.
Smectics typically have higher viscosities than standard nematics because of the
layered structure. The three most significant smectic phases are Smectic A (SmA),
Smectic C (SmC), and Chiral Smectic C (SmC), respectively (Gray and Goodby
1984; Khan et al. 2021). Ferroelectric LC phases are found in molecules containing
one or more chiral centers, and chirality of the molecules is translated to the chirality
of the macroscopic mesophase, forming a helical, chiral assembly. The generated
helix’s pitch is temperature-dependent, and the helical structure’s handedness
depends on the presence of a chiral center since one enantiomer produces a left-
handed helix while the other produces a right-handed helix (Takanishi 2020; Moriya
et al. 2021). Compared to equivalent achiral phases, the symmetry is reduced when
chirality is introduced into a mesophase. Chiral mesophases frequently exhibit steric
effects that reduce phase stability and lower clearing points (the temperature at
which a mesophase transitions to an isotropic phase) (Saupe 1973; Gray and Goodby
1984; Sebastián et al. 2022). Discotic mesogens are disk-shaped, inflexible, flat,
symmetrical, aromatic cores with an aliphatic chain perimeter. They can generate
either columnar or nematic mesophase. Throughout the sample, the molecules in the
discotic nematic phase freely disperse. Columnar phases, in which molecules collect
into columns that further organize to produce various two-dimensional columnar
assemblages, are the most frequently encountered discotic phases (Chandrasekhar
et al. 1977; Percec et al. 2022).
The bent-core (boomerang, bow) mesogens are another name for these
banana-shaped LCs. These molecules are bent-core mesogens with an anisotropic
form that differs from the classical disk and rod-shaped molecules. Examples are
1,3-disubstituted benzene, 3,5-disubstituted 1,2,4-oxadiazoles, and 2,5-disubstituted
1,3,4-oxadiazole. The first ferroelectric and antiferroelectric LCs without chiral
carbon are banana-shaped LCs. When molecules have bent cores, steric packing is
preferred because it creates layers with polar axes that are defined by molecules’
“bows” pointing in the same direction. This polar order is responsible for the
macroscopic chirality of the bulk structure as well as the ferroelectric characteristics
of the switchable B2 and B5 crystals. Mesogens in the shape of bananas display a
wide range of liquid crystalline states; these compounds display both banana and
typical mesophase. It was later established that it had antiferroelectric switching
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Oxadiazole as Liquid Crystals 47
capabilities. These compounds often display the nematic and Bn (B1, B2, ... ) phases.
The phases will depend on the bond angle between the center rings of the LCs; if the
bond angle is lower, it will display nematic phases, and if the bond angle is higher, it
ZLOOGLVSOD\VPHFWLFSKDVHV6RILDHWDO6LPLüHWDO
4. Oxadiazole as Liquid Crystals
Synonymously called “mesogen,” liquid crystals (LCs) are of great interest to both
research and industry because they are synthesized when the properties of two states
of matter—solid and liquid confluent (Santos et al. 2021). They have the flexibility
of translation between solids and liquids and orientational order, longer shelf life,
and are thermodynamically stable (Tschierske 2013). Because of their propensity
to align along the axis, LCs have an anisotropy property that is unique for liquids.
The loss of orientational order is seen when a molecule has formed anisotropy and
such molecules do not undergo a single transition from solid to liquid on heating
but rather a series of transitions. The melting point is the first temperature at which
a solid enters a phase known as the mesophase. A clearing temperature is when a
solid maintains the isotropic phase (Bushby et al. 2013; Han et al. 2018). Due to
their unique properties, they are widely recognized as organic semiconductors for
the fabrication of efficient, ultra-lightweight, low-power-consuming, low-cost, and
flexible components for electrical devices. As a result, new liquid crystal molecules
are becoming increasingly popular. Adequate molecular planning is essential
to suggest a synthetically feasible structure with the necessary properties. In this
context, oxadiazole, the five-membered heterocycles, played a significant role in
fabricating more durable materials with various polarities and geometries. Their ease
of synthesis tuned physical and chemical, thermal stability, mesomorphic behavior,
and high luminescence quantum yield are excellent LCs. This is because their unique
structure is equipped with several mesogenic cores, including calamitic, bent cores,
polycatenar, and discotic (Ghosh and Lehmann 2017; Kotian et al. 2020; Santos
et al. 2021).
It was first discovered in 1888 when Friedrich Reinitzer noticed that cholesteryl
benzoate had two melting points in the beginning. At 145°C, the substance was turbid,
and at 178.5°C, it turned translucent (Reinitzer 1888). Then, Otto Lehmann used a
polarizing microscope to study cholesteryl benzoate in 1889 and concluded that it
existed in a new state of matter at this temperature range. He then came up with the
phrase “liquid crystal.” The term “mesomorphs,” was proposed by George Friedel.
Rinne attempted to rename them as “Paracrystals” in 1933, and Bernal demonstrated
in 1951 that naturally occurring LCs are connected to biological processes. Although
their behavior is described by the names “anisotropic liquids,” “mesomorphic,” or
“mesophases,” the term “LCs” has gained popularity (Kotian et al. 2020).
5. Mesomorphic Features
Oxadiazoles are five-membered heterocycles with one oxygen and two nitrogen
atoms. They provide a wide range of biological applications, such as anticancer,
anti-inflammatory, antimycobacterial, anticonvulsant, antibacterial, antifungal,
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48 Oxadiazole in Material and Medicinal Chemistry
hypoglycemic, and antiparasitic drugs (Kotian et al. 2020). The most popular methods
for producing 1,3,4-oxadiazole include the oxidation of acyl hydrazones (Nandeesh
et al. 2016), thermal or acid-catalyzed cyclization of diacyl hydrazines (Patel et al.
2014), and chloramine-T oxidative cyclization of semicarbazones (Rai et al. 1995).
A new series of 2,2-bis (3,4,5-trialkoxyphenyl)-bi-1,3,4-oxadiazole were
synthesized and investigated their mesomorphic behavior. The compound showed
Col mesophases at room temperature (Qu and Li 2007). Several non-symmetrical
1,2,4-oxadiazole derivatives’ thermal and optical characteristics were extensively
studied, showing SmC and N phase behavior. Their mesophase ranges are broad
with low melting points (Gallardo et al. 2020). Sung and Lin synthesized a group
of compounds with a 1,3,4-oxadiazole moiety containing Me, OMe, Cl, F, CN, and
NO
2
. Groups and investigated the properties of the liquid crystals. The derivatives
displayed a stable SmA, SmE phase. It was observed that the mesomorphic phases,
internal quantum efficiencies, optical characteristics, and transition temperature are
significantly influenced by terminal substituents (Kotian et al. 2020).
In the presence of pyridine, amidoxime and acyl chlorides can be combined
to synthesize 1,2,4-oxadiazole (Chiou and Shine 1989). Oxadiazole-containing
bent-shaped LCs were successfully synthesized using NO
2
groups as lateral
substituents and C’C groups as connecting groups. The transition temperature
decreased with the addition of the terminal NO
2
group, and the Sm phase was
discovered to be present (Cristiano et al. 2005). 1,3,4-oxadiazole derivatives were
synthesized using thiophene heterocycles, and their mesomorphic characteristics
were investigated (Han et al. 2008). The derivatives with the longer alkoxy chain and
terminal electron-withdrawing group displayed the SmA phase. They also concluded
that terminal groups impact the formation of mesophases. Upon cyclo condensing
amidoximes with trifluoroacetic anhydride, 3,5-disubstituted 1,2,4-oxadiazole
compounds were synthesized (Guo et al. 2014). The chemical names displayed N
and/or Sm phase for different derivatives. By reacting 4-benzyloxybenzonitrile with
hydroxylamine hydrochloride, bent-shaped LCs containing 1,2,4-oxadiazole have
been synthesized, which produced the appropriate amidoxime and further the desired
product (Shanker and Tschierske 2011). Also, 4-[3-(4-benzyloxyphenyl)-1,2,4-
oxadiazol-5-yl] phenyl 4-hexyl benzoate was obtained on reacting with 4-(4-n-hexyl
benzoyl oxy) benzoic acid which showed an enantiotropic N phase. A new
series of 1,3,4-oxadiazole derivatives were synthesized, and their mesomorphic
characteristics were investigated. The synthetic materials showed the Colh phase,
chirality, OH group, and dependency of the mesomorphic features on the aliphatic
chain connected to the rigid disk. The Colh phase of the compound persisted even at
ambient temperature (Girotto et al. 2014). Using TG-MS-FTIR, the thermal stability
of LCs containing derivatives of 1,3,4-oxadiazole Schiff bases with alkyloxy and
acyloxy terminal chains was investigated. The compounds had good thermal stability
and could tolerate temperatures up to 330 °C. When compared to acyloxy analogs,
it was discovered that compounds with the alkoxy terminal chain had improved
thermal stability (Lisa et al. 2011).
Star-shaped 1,3,4-oxadiazole derivatives with alkoxy substitutions were
synthesized in conjunction with phenyl ethynylenes. Enantiotropic Col mesophase
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Oxadiazole as Liquid Crystals 49
was present in the discotic molecules that were produced. The compound with a
C12 alkyl chain changes into a glassy film with LC characteristics that remained
stable for over a year. It is also thought to be a strong contender for displays and
non-doped blue-emitting diodes (Prabhu et al. 2012). Phenylene bis-1,3,4-oxadiazole
group-containing LCs were synthesized, which showed the characteristics of typical
LCs (Chai et al. 2008). Ten novel 1,2,4-oxadiazole bent-rod-shaped compounds
were synthesized with polar substituents like nitrogen dioxide (NO
2
), hydroxy
(OH), amino (NH
2
), and iodine (I) on the central core exhibited LC characteristics.
Compounds substituted with NO
2
, and I lacked mesomorphic properties. Despite
having a bent form, compounds showed the Colh phase. It might be due to the
hydrogen bonding, steric interactions, and dipoles that result in the dimer, trimer,
and tetramer inside a single disk and enable the formation of a Colh phase (Kotian
et al. 2020). The 1,3,4-oxadiazole compound, containing gallic acid, was
synthesized to study their liquid crystalline characteristics. The compound showed a
crystal-to-isotropic transition and exhibited monotropic Colh, which made it evident
that the terminal alkyl chain influences how the LC behaves. It was claimed that the
produced compounds have improved thermal stability, which makes them suitable
materials for organic electronics (Frizon et al. 2014).
In order to study the behavior of 2,5-disubstituted [1,3,4]-oxadiazole in
polycatenars 2,5-bis4-[(E)-2-(3,4-diakoxyphenyl) vinyl] phenyl-1,3,4-oxadiazoles
were synthesized. Tetracatenar oxadiazoles, dicatenar oxadiazoles, and hexacatenar
oxadiazoles all showed lamellar phase, whereas the dicatenar oxadiazoles showed
only Col phase. Two phenylenevinylene groups in the tetracatenar caused lamellar
phases. As the number of chains increased from dicatenars to tetracatenars to
hexacatenars, a drop in the transition temperature was seen (He et al. 2007). Several
nonsymmetric compounds with 1,3,4-oxadiazole and biphenyl units and various
terminal chains were synthetically produced. The derivatives showed either N or
SmA mesophase. It was discovered that the mesophases were caused by the electrical
characteristics of terminal groups, such as UV-Vis absorption and photoluminescence
(Han et al. 2010). Boomerang-shaped LCs containing 2,5-bis(p-hydroxyphenyl)-
1,3,4-oxadiazole showed LC characteristics. P-Dodecyloxyphenyl tails were used
to replace the mesogenic core, and the outcome was polymorphism with five
SKDVHV16P&6P;6P<DQG6P='LQJHPDQVDQG6DPXOVNL%DUEHUá
and colleagues synthesized and studied a unique series of LC materials based on
1,3,5-benzenetrisamide trioxadiazole derivatives with varied side alkoxy chains.
They have documented how mesophases depend on various terminal alkoxy chains.
Nine alkoxy chains were reported to exhibit the Col phase, while compounds with
six alkoxy chains displayed the Colh phase (Barberá et al. 2011).
By treating 3-(4-pyridyl)-5-(4-n-alkoxy) phenyl-1,2,4-oxadiazoles with benzoic
acid, 4-chlorobenzoic acid, or 4-methylbenzoic acid, the LCs were created. It was
noticed that oxadiazole or carboxylic acid did not exhibit any mesomorphic features.
But LC behavior was visible when they were joined together through H-bonding
(Parra et al. 2005). Lin and co-workers synthesized a new set of mesogens carrying
1,3,4-oxadiazole and thiophene and displayed the Colh phase (Lin et al. 2015). Tomi
and co-workers synthesized and characterized two series of ester compounds based
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50 Oxadiazole in Material and Medicinal Chemistry
on the two isomers of the oxadiazole ring. On cooling in a specific range, some
derivatives of the 1,2,4-oxadiazole isomer showed monotropic N mesomorphism.
The 1,3,4-oxadiazole derivatives that were synthesized, however, were discovered
to be non-mesomorphic. They concluded that the bending angles of the oxadiazole
derivatives substantially influence mesomorphic characteristics (Tomi et al.
2017). Another study investigated the impact of the terminal alkoxy chains in the
1,2,4-oxadiazole core, which had both ester and ether linkages inside the same
molecule. They concluded that the length of the terminal alkoxy chain did not affect
the character of mesophase (Ali et al. 2017).
Kang and co-workers synthesized bent-shaped molecules with varied side
chains. Polymorphism was discovered in oxadiazole derivatives, including calamitic
N and SmC phases and the banana Bx phase (Kang et al. 2006). In another study, a
series of polycatenar-based LCs containing bis-1,3,4-oxadiazole were investigated
to study their liquid crystalline characteristics, which exhibit the Colh phase (Kotian
et al. 2020). Based on oxadiazole bis aniline, the synthesis of bent-core LC molecules
was reported, and their phase behaviors were investigated. Three distinct alkyl chains
were used to create three different molecules. Compounds that have terminal hexyl
and terminal octyl chains only display N phases, whereas compounds with terminal
dodecyl alkyl chains only display SmC, SmX, and SmY phases, respectively (Kotian
et al. 2020).
Saha et al. (2017) created the asymmetrical hockey stick-shaped mesogenic
molecules with 1,3,4-oxadiazole as the central core component and a lateral methoxy
group. The monotropic N phase was present in compounds with shorter alkyl chains,
but the SmA phase was present in the extended derivative. Abboud et al. (2017)
explored a similar series with the terminal nitro group and the mesogenic core
1,3,4-oxadiazole. While compounds with longer-terminal alkoxy chains displayed
the SmA phase, those with shorter-terminal alkyl chains displayed the N phase.
Al-Obaidy et al. (2017) investigated several 1,3,4 and 1,2,4 oxadiazole derivatives
with various para-substitutions (CN, COOCH
3
, OCH
3
, NO
2
, Cl). They discovered
that several groups contributed to the molecule’s mesogenity in various ways.
SmA, N, and SmC phases could be seen in every derivative that was produced. The
mesomorphic properties of 1,3,4- and 1,2,4-oxadiazoles were also studied, and it was
discovered that 1,3,4-oxadiazole derivatives lack LC features.
The impact of lateral halogen substitutions in bent-core LCs with oxadiazole
rings was described by Nguyen et al. (2015). When the compounds with one halogen
and two methyl groups reached room temperature, they displayed the N phase.
When halogens were substituted, the N phase persisted and changed to the isotropic
phase upon further heating. The synthesis and mesomorphic behavior of tris- and
bis-(1,3,4-oxadiazoles) with peripheral quinoxalines were reported by Lin and Lai
(2016). The compounds exhibited phase crossover in the temperature range between
the rectangular and hexagonal Col phases, which displayed Colr at low temperatures
and Colh at high temperatures. They explained it away as being caused by the
hefty quinoxaline necklace. A new series of 4-[5-(p-tolyl)-1,2,4-oxadiazol-3-yl]
phenyl substituted benzoate derivatives were synthesized by Ali and co-workers
and investigated the impact of terminal substituents on LC characteristics (Ali
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Oxadiazole as Liquid Crystals 51
et al. 2019). The para-substituted compounds displayed an enantiotropic N phase
over a broad temperature range. In order to study their potential use as dopants
in blue phases (BPs), Yu et al. (2019) developed bent-shaped light-responsive
azo-oxadiazole derivatives. When compared to straight terminals, they discovered
that synthetic derivatives with branching terminals had greater miscibility in the
host LC. They also looked at how the rigid core’s length affected the BP range and
discovered that as it got longer, the rigid core’s temperature range likewise grew.
The 1,2,4-oxadiazole linked to thiophene was synthesized by Girotto et al. (2016)
and showed mesomorphic behavior. They noticed that the increase in the number
of chains on the symmetrical and non-symmetrical compounds did not favor the
mesomorphic behavior, most likely due to the rise in volume. Mesomorphism in
the N phase was also seen in compounds when triple bonds were used as spacers
instead of the 1,3,4-oxadiazole in combination. This compound produced a more
ordered SmC phase and N phase, and a lower melting temperature was also noted.
Furthermore, 1,3,4-oxadiazoles derivatives were synthesized by Kuo et al. (2016),
who also studied their mesomorphic behavior. The limited mesophase temperature
range and higher clearing temperatures were present in all the synthetically produced
derivatives’ N or/and Sm phases. In one of their schemes, Choi et al. (2011) reported
synthesizing a new series of 1,3,4-oxadiazole derivatives and investigated their LC
characteristics. They also detailed the synthesis of 1,3,4-oxadiazole derivatives with
lollipop shapes. Derivatives that combined rod- and disk-shaped mesogen produced
monotropic discotic Col mesophase.
Oxadiazoles are one of the most widely used heterocycles in LCs among the
five-membered heterocycles. Due to the simplicity of synthesis, there are
numerous papers on the synthesis and mesomorphic investigations of 1,3,4- and
1,2,4-oxadiazoles. When mesomorphic studies are considered, it is discovered that
1,2,4-oxadiazoles exhibit better mesomorphic features, indicating the importance of
the bending angle. When joined to substituted phenyl rings and another five-membered
heterocyclic ring, 1,3,4-oxadiazole rings display mesomorphism. Mesophase types
include banana mesophases, discotic or Col mesophases, and traditional calamitic
mesophases (N, SmA, and SmC).
6. Conclusion
The applications of LCs, which are intriguing materials, are used in a variety of
scientific fields, including physics, chemistry, arithmetic, biology, and technology.
They are frequently used in the fabrication of devices for various applications. Due
to its asymmetric electron cloud distribution, the 1,2,4-oxadiazole is a promising
core to display “B” phases. The 1,2,3, 1,2,4, 1,2,5, and 1,3,4-oxadiazoles exhibit
remarkable biological and physiological properties. The oxadiazole derivatives
have also been noted to be effective OLEDs, photovoltaic, and EL devices. It has
been widely acknowledged that there has been a significant advancement in the
structure-property connections of liquid crystalline 1,3,4-oxadiazole derivatives. The
1,3,4-oxadiazole unit, one of the most significant synthons, has been extensively
employed to create numerous LCs with different mesophases, such as uniaxial
nematic, smectic, columnar phases and even the elusive nematic phase with
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52 Oxadiazole in Material and Medicinal Chemistry
biaxiality. But there are still a lot of scientific questions in this area that require
inquiry, and research needs thorough investigations. Last but not least, even though
numerous liquid crystalline 1,3,4-oxadiazole derivatives have been developed, most
of them are used for theoretical and basic research. Future research into the practical
application of novel materials must be considerably expanded.
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the liquid crystalline properties of the new synthesized 1,2,4-oxadiazole derivatives. Sci. Technol.
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Ali, G. Q. and I. H. R. Tomi. 2018. Synthesis and characterization of new mesogenic esters derived from
1,2,4-oxadiazole and study the effect of alkoxy chain length in their liquid crystalline properties.
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